Method and apparatus for coating a lithographic plate



G. S. ROWELL Dec. 25, 195] METHOD AND APPARATUS FOR COATING A LITHOGRAFHIC PLATE Filed Feb. 25. 1947 Patented Dec. 25, 1951 METHOD AND APPARATUS FOR COATING A LITHOGRAPHIC PLATE George S. Rowell, Bedford, Ohio, assigner to The Chandler & Price Company, Cleveland, Ohio,

a corporation of Ohio Application February 25, 1947, Serial No. 730,833

10 Claims.l (Cl. 117-101) requiring considerable skill and experience on the .j

warm air upon the center of the plate causing the solution to dry thereon.

' Several difficulties are encountered in preparing satisfactory plates in accordance with the above described method employing prior art machines. IThe solution being .dropped vertically centrally of the spinning plate tends to form bubbles which may be imprisoned in the coating as it dries. The distribution of the solution in a thin film over the plate through the action of centrifugal force and the current of warm air directed thereagainst tend to Acause the formation of small waves in such film as it dries so that the finished plate is not evenly coated. When the plate is later exposed the thicker portions of the film will be incompletely exposed resulting in only partial ainity for ink, and a grayish, mottled, or ghosted image will be obtained on printing. If the plate be exposed long enough to ensure proper exposure of the thicker portions of the lm then the thinner portions will be overexposed and become enamel-like and brittle, failf ing to hold ink well. Thicker portions of the coating'lm whichhave been insufciently exposed do not adhere well to the plate and tend to Walk and peel.

Since the solution is fed to the center of the` plate and -dries progressively as it flows outwardly the nlm tends to be thickest about the perimeter and thinnest at the center of the plate. This thin center portion may be over-exposed in the printing and may also be somewhat affected by s' It is, therefore, a primary object of my invention to provide a new and improved lithographie coating machine operative vto produce lithographic plates of uniformly high quality.

It is a further object of my invention to provide such machine which will produce a lithographic plate having a coating of uniform thickness and sensitivity.

It is another object of this invention to provide such machine which will be capable of rapid operation by one not overly skilled in the art and which may be readily cleaned.

Other objects of the invention will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, said invention then comprises the l features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

In said annexed drawing:

Fig. 1 is a vertical sectional view of one form of lithographie coating machine constructed in accordance with my invention;

Fig. 2 is a top plan view, partly in section, taken along the line 2- -2 on Fig. l; and

Fig. 3 is a fragmentary elevational View showing a cleaning device secured to the edge of the turntable of my machine.

Referring now more particularly to such drawing, the supporting frame of my new machine comprises a base I from which four legs 2, 3, 4 and 5 rise to support an annular trough E. A drive shaft 1 is vertically journalled in a thrust bearing in central column 8, and is adapted to rotate cicrcular turntable or platform 9, the upper end of such shaft being keyed in stud I0 centrally disposed on the lower side of such turntable. Such turntable is itself supported on roller bearings II in bracket I2 on such column, and is adapted to be driven through bevel gear I3, worm I4, pulley I5, belt i6, adjustable pulley I1, belt I8, and electric motor I9. Pulley I'l and motor AI 9 are mounted on flanged plate member 20, such motor being additionally securedto leg 5 Heating coils 2| are laid in an annular chan nel 22 within the inner periphery of trough S, such channel being supported by branchesv 23 of the main frame legs. While such heating coils will preferably comprise electric resistance members, gas burners may be employed if desired. Substantially radially disposed vanes 24 depend from the underv surface of turntable 9-fabove nular baie 28 depends from such cover beneath`- such outlet ports, causing the'heatedairtofollow the path generally indicated by theT arrowsA in Fig. 1.

A graduated container 29 is mounted-centrally on such cover, communicating byway of stopcock 38 with curved tube 3| from which the coating solution may be dispensed in regulated flow. A stopcock 32 is provided in the bottom of trough 6 through which any excess solution may bewithdrawn.

Iri'operation, the plate to be coatedisplaced centrally on turntable 9 and the turntable` is revolved. The speed atwhich such turntable re'- volves, the amount of solution dispensed from container 28,' and the temperature of.' the heated air which passes over the surface of'theplate determine they thickness of theI coating obtained. The outwardly curved end of'f'tub'e' 3|v feeds the solution in the direction it will be spreadv byv action of centrifugal force, eliminating bubble formation at this point. The heated air'passes inwardly over the plate in adirection contrary to the flowof solution thereover, preventing the formation of waves in the coating film. If desired, the warm air may be supplied from another source, the important thing being that it be caused to flow inwardlyv over the plate` being coated;

The downturned lip 25 of theturntable facilitatesv drainage ofy excess coating solution into trough 6 from which it may be drained through stockcock` 32. After removal of the plate for further drying the turntable and trough mayy be iiushed off with water or cleaning solution before coating another plate. As a result there isno residue which might otherwise come into contact with the next plate toV be coated' and spoil the surface thereof;

After the plate has dried it is ready to be" placed in a printing frame to receive an image from a photographic negative, for example.

As shown in Fig. 3 of the drawing I provide a special cleaning device adapted to bev secured to the edge ofk turntable 9 by means of clamp 33; A container- 3ft of water or other cleansing uid is supportedby said clamp adapted to flow through tube35'into trough 6 in advanve of' air scraper or squeegee attachment 36 havinga rubber edge portion 3"?. Such attachment, revolving with-turntable 9, cleanstrough S of excess coating solution through stock-cock 32'. Unless such solution is regularly removed it becomes sour-smelling and water insoluble.

Tube 3l leading from container 29 may desirably pass through a slotV in cover 26 tio-permit slight radial adjustment'of" its position;

Other modesV of' applying the principleofthe invention may be employed, change being made an annular trough supported below said downturned fiange of said turntable and having its outer side edge extending upwardly past said turntable, vanes on the under surface of said turntable adapted to force air outwardly between said downturnediiange and trough, a cover engaging the outer side edge of said trough and enclosing said turntable adapted to direct a current of air substantially radially inwardly over the fentire'upper surface of said turntable simultaneously, air outlet openings in said cover only adjacent the-center thereof, a coating solution container supported centrally of said cover, an outlet for said container directed substantially radially' overf thevicenter of said turntable, and annular heating means beneath said turntable adapted 'to heat said air. prior to its passage over said turntable.

2. In alithographic coating' machine,.a` turntable, vanes-on the under surface ofsaidV turntable adapted. to forceva current of air outwardly therefrom, substantially airtight'en'closing means adapted to receive and direct the entire current of air substantially radially inwardly over the surface of said turntable uniformly simultaneouslyv from' about the entire periphery' of the latter, an air outlet' in said enclosing means, posi'- tioned above and generally centrally offsaid turntable, and annular heating means beneath said turntableY adapted to heat said air prior to'.l its passage over said turntable.

3. In a lithographieV coating machine, a turntable, vanes on the under surface of said turntable adapted to force a current of air outwardly therefrom, turntable enclosing means adapted and disposed to-receive and direct the current ofv air substantially radially inwardly over the upper surface of said turntable uniformlysimultaneously from about the entire periphery of the latter, air outlet means in said enclosing means positioned abovev and generally centrally of said turntable, and means adapted to heat said air prior toits passage over said turntable.

4. l'nla lithographic coating machine, a turntable',v meansr operative to blow a current of air substantially radially inwardly over the surface of' said turntable continuously uniformly from aboutiY the entire periphery thereof, enclosing means adapted to conne said current of air over said turntable, air outlet means in said enclosing means positionedabove and generally centrally of said turntable, and means adapted tof-heat: said air prior to its passage over said turntable.

5. The method of coating a lithographie plate toform' a coating of' substantially uniform thickness which comprises rapidly revolving said plate horizontal' plane about an axis generally centrally thereof, pouring a coating liquid centrally on said revolving plate whereby said liquid willr be spread under influenceV of centrifugal force', causing a current of air to flow uniformly radially inwardly over such revolving plate from about the entirev periphery of the latter during application of'said' liquid to dry said liquid, and removing said air from the center surface of Saidplate upwardly along theaxis ofy rotation.

6. In a lithographie coating machine, a turntable adapted to support a lithographie. plate thereon,` means adapted to dischargev coating liquid on said plate substantiallyy centrally of said turntable, turntable enclosing meansv adapte'd to direct a currentof' air substantially radially inwardly only across the uppersurf'ace of said plate and said turntable uniformly and simultaneously from about the entire outer periphery of the latter, air inlet means circumferentially of said turntable, and an air outlet positioned in said turntable enclosing means above and generally centrally of said turntable.

7. In a plate coating machine, a flat turntable adapted to support a plate having a fluid coating thereon, means operative to blow air substantially radially of the axis of rotation of said turntable inwardly over the surface of said turntable and plate uniformly simultaneously from about the entire outer periphery of said turntable, and means operative to remove said air from the center surface of said turntable upwardly along the axis of rotation of said turntable.

8. In a plate treating machine having a turntable adapted to support a plate having a uid coating thereon, drive means operative to rotate said turntable, and means adapted to deliver a current of heated air simultaneously to the entire outer periphery thereof, the combination of a housing arranged and disposed over said turntable to direct the current of heated air substantially radially inwardly across the plate-supporting surface thereof uniformly simultaneously from about the outer periphery of the turntable, air inlet means circumferentially of said turntable to which said heated air may thus be delivered, and an air exit opening in said housing positioned above and generally centrally of said turntable through which said air may escape after thus passing radially inwardly thereacross.

9. The method of coating a lithographie plate to form a coating of substantially uniform thickness which comprises rapidly revolving said plate in its own plane, delivering a coating liquid onto a surface of said revolving plate and spreading said liquid thereover through action of centrifugal force, causing a drying current of air to flow radially inwardly from the entire periphery of said plate over the surface of said plate toward the axis of rotation during spreading of the liquid, whereby the flow oi air is uniformly counter to the spreading iiow of the liquid and tends to prevent the formation of the usual waves in the coating and removing said air from the center surface of said plate upwardly along the axis of rotation.

10. The method of coating a lithographie plate to form a coating of substantially uniform thickness which comprises depositing a coating liquid on a surface of said plate adapted when dried to form the desired coating, revolving said plate in its own plane and thereby spreading said liquid thereover through action of centrifugal force, causing a drying current of air to flow from about the entire periphery over the surface of said revolving plate in a direction counter to the spreading flow of the liquid to dry the coating while substantially preventing the formation of the usual waves therein and removing said air from the center surface of said plate upwardly along the axis of rotation.

GEORGE S. ROWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,059,057 Mason Apr. 15, 1913 1,253,990 McCue Jan. 15, 1918 1,343,887 Slocum June 15, 1920 1,592,608 Lorenz July 13, 1926 2,021,485 Huebner Nov. 19, 1935 2,074,171 Fritsche Mar. 16, 1937 2,084,642 Henderson June 22, 1937 2,234,608 Robinson et a1 Mar. 11, 1941 2,257,373 Fanselow Sept. 30, 1941 2,386,591 Campbell Oct. 9, 1945 2,387,349 Powers Oct. 23, 1945 2,455,761 Hacker Dec. 7, 1948 FOREIGN PATENTS Number Country Date 625,958 Germany Feb. 18, 1936 

5. THE METHOD OF COATING A LITHOGRAPHIC PLATE TO FORM A COATING OF SUBSTANTIALLY UNIFORM THICKNESS WHICH COMPRISES RAPIDLY REVOLVING SAID PLATE IN A HORIZONTAL PLANE ABOUT AN AXIS GENERALLY CENTRALLY THEREOF, POURING A COATING LIQUID CENTRALLY ON SAID REVOLVING PLATE WHEREBY SAID LIQUID WILL BE SPREAD UNDER INFLUENCE OF CENTRIFUGAL FORCE, CAUSING A CURRENT OF AIR TO FLOW UNIFORMLY RADIALLY INWARDLY OVER SUCH REVOLVING PLATE FROM ABOUT THE ENTIRE PERIPHERY OF THE LATTER DURING APPLICATION OF SAID LIQUID TO DRY SAID LIQUID, AND REMOVING SAID AIR FROM THE CENTER SURFACE OF SAID PLATE UPWARDLY ALONG THE AXIS OF ROTATION. 